Rhesus macaques are exceptionally adapted to coexisting with human and thrive near human settlement in both urban and agricultural areas. There are numerous populations of non-human primates (Macaca mulatta) living in and around the Raj-Gardh fort Dumraon, Buxar but none have been documented. A survey of Raj-Gardh Garrison monkey M. mulatta was carried out and studied its ecology and behavior during January 2013 to December 2014 in Dumraon. Macaque position in the group was observed based on the rank and “central male subgroup” together with two or three oldest males that was observed most dominant. Troop also co-dominant, along with females, their infants and juveniles. The home ranges of this species M. mulatta were observed between .01 to 2.5 km2 in day. Feeding activity was found mostly during morning & evening time and resting between 10 AM to 3 PM when temperature was high. M. mulatta is sexually dimorphic with males and females both have represented separate hierarchies. The rhesus groups were characterized by female philopartry with residue natal group but male dispersal. Mating observed mostly in the month of November to January and infants handled by close female relatives and protected by adult males. In the first few days the infant was carried ventrally by the mother. Loss of natural habitat and increased conflict between human and non-human primates were found to be the major threat for the Raj-Gardh Macaques of the region.